19 week old hens losing feathers; no eggs yet and no roosters

What in the world should I be looking for on my hens that are losing feathers. My RIR is losing her beautiful green tail feathers and I've noticed by Black Maran is losing feathers but have no bare spots. I'm finding feathers everywhere. I've checked them for mites and other buggies but their skin looks good and healthy. None of them have layed eggs yet and I just got rid of a rooster that I thought was a hen. I just switched them from grower to layer and they are allowed to forage in the backyard. I keep their coop clean and change their water everyday. Since I'm in Texas, could it be the heat? I keep pans of water around for them and they love walking through them. What could I be doing or what do I need to do. I am a newbie and love all five of my girls.